Synthesis, temperature behavior, and hydrolytic stability of Na-Zr and Ca-Zr phosphate molybdates and phosphate tungstates

We have synthesized Na1 ¿ xZr2(PO4)3 ¿ x(¿O4)x and ¿a0.5 ¿ xZr2(PO4)3 ¿ x(¿O4)x (X = Mo, W; 0 ¿ x ¿ 0.5) compounds with the NZP structure. Their thermal expansion has been studied in the temperature range 25¿800°C using high-temperature X-ray diffraction and shown to have a tendency to decrease as the occupancy of the extraframework sites in their structure decreases. Ceramic samples with a relative density above 97.5% have been prepared from the synthesized phosphate molybdates and phosphate tungstates by spark plasma sintering. Their strength characteristics (microhardness and fracture toughness) have been determined and they have been characterized by hydrolytic stability tests.